Method and apparatus for forming a hollow FRP article by internal pressure molding

ABSTRACT

A method for forming a hollow FRP article by internal pressure molding includes positioning a FRP prepreg on a periphery of an airtight internal-pressure holding tube, inserting a composite body including the internal-pressure holding tube and the prepreg into a vacuum chamber containing a forming die, evacuating the vacuum chamber in an isolation state where the composite body and the forming die do not contact each other, and clamping the forming die to bring the forming die and the composite body into contact with each other and heating the forming die with an application of pressure to an inside of the internal-pressure holding tube after completion of the evacuating step.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and an apparatus forforming a hollow FRP (fiber reinforced plastic) article such as a golfclub shaft, a ski pole, a fishing rod or a hockey stick by internalpressure molding.

[0003] 2. Description of the Related Art

[0004] Internal pressure molding (IPM) is often adapted for forming ashaft such as a golf club shaft. In the molding process, a mandrel iscovered with an internal-pressure holding tube (bladder), a prepreg madeof a sheet FRP is put on the mandrel covered with the internal-pressureholding tube, the composite body that is composed of the mandrel, thebladder and the prepreg is set in a shaft forming die, and the shaftforming die is heated while the prepreg and the shaft forming die arebrought into intimate contact with each other by applying pressure tothe inside of the internal-pressure holding tube to increase theinternal pressure thereof. The mandrel is either used as an air passageduring the heating of the shaft forming die, or removed after theaforementioned composite body is completed so that an air-injectingmouth piece, which is provided independently of the mandrel, can befixed to an open end of the internal-pressure holding tube.

[0005] However, in the above-described internal pressure moldingprocess, the air exiting a space between the shaft forming die and theprepreg prevents the shaft forming die and the prepreg from being inintimate contact with each other. This makes it impossible to obtain asatisfactory surface irregularity (surface roughness) of the prepreg. Toprevent this problem from occurring, the assignee of the presentinvention has applied a vacuum forming method (which is a known formingmethod in which the air in a forming die is evacuated to a degree ofvacuum), which is often used as a vulcanization forming for rubbermaterial, in an internal pressure molding process. Nevertheless, it hasstill proved difficult to achieve a satisfactory surface irregularity.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method and an apparatus forforming a hollow FRP article (such as a golf club shaft) with asatisfactory surface irregularity by applying a vacuum forming method inan internal pressure molding process.

[0007] As a result of investigating the cause of the inability ofachieving a satisfactory surface irregularity even if a vacuum formingmethod is applied in the internal pressure molding process, it wasestablished that air remains in the space between the forming die andthe prepreg even if the forming die is evacuated with theprepreg-composite body being set in the forming die, and that theremaining air causes deterioration in the surface irregularity, e.g.,causes pits and dimples on a surface of the molded hollow article. Thepresent invention has been devised in view of this problem, based on thefinding that the surface irregularity is drastically improved if theforming die is evacuated with the forming die and the prepreg does notcontact the forming die (i.e., with the prepreg-composite body floatingin the forming die).

[0008] According to an aspect of the present invention, a method forforming a hollow FRP article by internal pressure molding is provided,including positioning a FRP prepreg on a periphery of an airtightinternal-pressure holding tube, inserting a composite body including theinternal-pressure holding tube and the prepreg into a vacuum chambercontaining a forming die, evacuating the vacuum chamber in an isolationstate where the composite body and the forming die do not contact eachother, and clamping the forming die to bring the forming die and thecomposite body into contact with each other and heating the forming diewith an application of pressure to an inside of the internal-pressureholding tube after completion of the evacuating step.

[0009] It is desirable for the prepreg positioning step to includecovering a mandrel with the internal-pressure holding tube, and wrappingthe FRP prepreg around the periphery of the internal-pressure holdingtube.

[0010] It is desirable for the clamping and heating step to includeapplying pressure to the inside of the internal-pressure holding tubethrough air passages formed on the mandrel.

[0011] It is desirable for the prepreg positioning step to includecovering a mandrel with the internal-pressure holding tube, wrapping theFRP prepreg around the periphery of the internal-pressure holding tube,and removing the mandrel after the wrapping step.

[0012] It is desirable for the clamping and heating step to includeapplying pressure to the inside of the internal-pressure holding tubethrough an air-injecting mouth piece fixed to an open end of theinternal-pressure holding tube after the mandrel is removed.

[0013] In another embodiment, an apparatus for forming a hollow FRParticle by internal pressure molding is provided, including a vacuumchamber, a forming die positioned in the vacuum chamber, avacuum-chamber opening/closing mechanism for opening and closing thevacuum chamber, a composite-body support device for supporting acomposite body without making the composite body come into contact withthe forming die in a state where the forming die is opened by thevacuum-chamber opening/closing mechanism, the composite body includingan airtight internal-pressure holding tube and a prepreg fitted on theairtight internal-pressure holding tube, an evacuation system forevacuating the vacuum chamber, an internal-pressure supplying device forapplying pressure to an inside of the internal-pressure holding tube ofthe composite body which is supported by the composite-body supportdevice, and a controller for actuating the vacuum-chamberopening/closing mechanism to clamp the forming die to thereby bring theforming die and the composite body into intimate contact with eachother, and for heating the forming die with an application of pressureto the inside of the internal-pressure holding tube after the vacuumchamber is evacuated by the evacuation system.

[0014] The composite body can be obtained by covering a mandrel with theinternal-pressure holding tube and wrapping the FRP prepreg around aperiphery of the internal-pressure holding tube.

[0015] The mandrel include an axial air passage and at least one radialair passage, and the internal-pressure supplying device can include anintermediate movable nozzle which is removably inserted into the axialair passage and includes a one-way valve for preventing air from flowinginto the vacuum chamber, a forced valve-opening nozzle which isremovably inserted into the forced valve-opening nozzle, the one-wayvalve being opened by an insertion of the forced valve-opening nozzleinto the intermediate movable nozzle, and an internal-pressure supplyingsource for supplying compressed air to the forced valve-opening nozzle.

[0016] The composite body can be obtained by covering a mandrel with theinternal-pressure holding tube, wrapping the FRP prepreg around aperiphery of the internal-pressure holding tube, and thereafter removingthe mandrel from the composite body.

[0017] The mandrel can include an axial air passage and at least oneradial air passage, and the internal-pressure supplying device caninclude an intermediate movable nozzle which is removably inserted intothe axial air passage after the removal of the mandrel from thecomposite body, and includes a one-way valve for preventing air fromflowing into the vacuum chamber; a forced valve-opening nozzle which isremovably inserted into the forced valve-opening nozzle, the one-wayvalve being opened by an insertion of the forced valve-opening nozzleinto the intermediate movable nozzle; and an internal-pressure supplyingsource for supplying compressed air to the forced valve-opening nozzle.

[0018] It is desirable for the composite-body support device to includea cantilever support base for supporting the composite body in acantilever fashion.

[0019] It is desirable for the composite-body support device to bemounted to a lower-die table which supports a lower die of the formingdie thereon. At least a part of the composite-body support device isbiased upwards, toward an upward moving limit thereof, by a biasingdevice so that the composite body, which is supported by thecomposite-body support device, does not contact the lower die.

[0020] The forming die and the composite body can be designed formanufacturing a golf club shaft.

[0021] The composite body can be obtained by covering a mandrel with theinternal-pressure holding tube and wrapping the FRP prepreg around aperiphery of the internal-pressure holding tube. The cantilever supportbase includes an inner support portion and an outer support portionwhich are positioned apart from each other in an axial direction of thecomposite body. It is desirable for the inner support portion to includea half-cylindrical recess having a radius corresponding to a half of anouter diameter of a large-diameter end of the mandrel, a portion of themandrel in a vicinity of the large-diameter end being positioned in thehalf-cylindrical recess. It is desirable for the outer support portionto include a cantilever through hole which is greater in diameter thanthe large-diameter end of the mandrel so that only an upper edge of theouter support portion in the cantilever through hole comes in contactwith the large-diameter end of the mandrel from above.

[0022] It is desirable for the composite-body support device to furtherinclude an anti-deflection support base, positioned inside the vacuumchamber, for subsidiarily supporting a small-diameter end of thecomposite body to prevent the small-diameter end from developingdeflections.

[0023] It is desirable for the lower-die table to be guided in avertical direction to be movable vertically with respect to an upper diefixed to an inner surface of the vacuum chamber.

[0024] The present disclosure relates to subject matter contained inJapanese Patent Application No.2003-090471 (filed on Mar. 28, 2003)which is expressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described below in detail withreference to the accompanying drawings in which:

[0026]FIG. 1 is a schematic axial cross sectional view of a compositebody which is made by wrapping a prepreg around a mandrel covered withan internal-pressure holding tube;

[0027]FIG. 2 is a cross sectional view taken along II-II line shown inFIG. 1;

[0028]FIG. 3 is a schematic system diagram including a cross sectionalview of an embodiment of an apparatus for forming a hollow FRP articleby internal pressure molding;

[0029]FIG. 4 is a perspective view of the apparatus shown in FIG. 3;

[0030]FIG. 5A is a cross sectional view of the apparatus shown in FIG.3, showing a forming process with the apparatus;

[0031]FIG. 5B is a cross sectional view of a portion of the apparatusshown in FIG. 5A;

[0032]FIG. 6 is a view similar to that of FIG. 5A, showing anotherforming process different from the forming process shown in FIGS. 3 and5A;

[0033]FIG. 7 is a view similar to that of FIG. 5A, showing anotherforming process different from the forming process shown in FIGS. 3 and5A and the forming process shown in FIG. 6;

[0034]FIG. 8 is a view similar to that of FIG. 5A, showing yet anotherforming process different from the forming process shown in FIGS. 3 and5A, the forming process shown in FIG. 6 and the forming process shown inFIG. 7;

[0035]FIG. 9 is a cross sectional view of a portion of an embodiment ofan internal pressure supply system for supplying compressed air into themandrel of the composite body, in a state where pressure is not yetapplied to the inside of the internal-pressure holding tube;

[0036]FIG. 10 is a view similar to that of FIG. 9, showing the portionof the internal pressure supply system in a state where pressure isbeing applied to the inside of the internal-pressure holding tube;

[0037]FIG. 11 is a cross sectional view taken along XI-XI line shown inFIG. 7;

[0038]FIG. 12 is a cross sectional view taken along XII-XII line shownin FIG. 7; and

[0039]FIG. 13 is a schematic cross sectional view of a composite body,wherein a mandrel is removed from the composite body after the compositebody is prepared using the mandrel, while an air-injecting mouth pieceis fixed to an open end of the internal-pressure holding tube instead.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040]FIGS. 1 and 2 show conceptual diagrams of an embodiment of acomposite body 10 which is constructed by covering a mandrel 11 in theshape of a tapered rod with an internal-pressure holding tube (bladder)12 made of a airtight rubber or plastic film, and subsequentlypositioning a prepreg 13 made of a synthetic resin sheet around theperiphery of the internal-pressure holding tube 12. The shape of themandrel 11 is simplified, and the diameter and the taper angle of themandrel 11 are exaggerated in the drawings. The mandrel 11 is providedin an axial center thereof with an axial air passage (axial throughhole) 11 a, and is provided with a plurality of radial air passages(radial through holes) 11 b which extend radially outwards from theaxial air passage 11 a. The mandrel 11 is provided in the vicinity of alarge-diameter end (butt end) thereof (the right end as viewed inFIG. 1) with an axial-movement prevention groove (circumferentialannular groove) 11 c. The internal-pressure holding tube 12 is in theshape of a long fingerstall, one end of which is formed as an open end,and is closely fitted on the periphery of the mandrel 11. The prepreg 13can be made to bulge by increasing the internal pressure of theinternal-pressure holding tube 12 by injecting compressed air into theaxial air passage 11 a of the mandrel 11. If necessary, the open end ofthe internal-pressure holding tube 12 can be prevented from bulgingexcessively by fitting a ring member on the open end of theinternal-pressure holding tube 12 or by holding the open end with aportion of a forming die. The prepreg 13 can be an FRP material whichcan be formed to have a strength enabling the prepreg 13 to be used as agolf club shaft by heating the FRP material to a predeterminedtemperature. Accordingly, the FRP material for the prepreg 13 does nothave to be of a specific type, and the ply number (number of wirings) ofthe material is optional. Note that the expression “to position aprepreg” is intended to be used to express all the cases of positioningthe prepreg on the periphery of an internal-pressure holding tube suchas a case of wrapping the prepreg around the periphery of aninternal-pressure holding tube or a case of attaching the prepreg to theperiphery of an internal-pressure holding tube in the specification andthe claim of the present invention.

[0041]FIGS. 3 and 4 show the overall structure of an embodiment of theapparatus for forming a hollow FRP article by internal pressure molding.This internal pressure forming apparatus is provided with a vacuumchamber 20 which is composed of a stationary base 20 a and a movablecase 20 b. The movable case 20 b can move toward and away from thestationary base 20 a via a vacuum-chamber opening/closing mechanism 21.In a vacuum-chamber closed state where the movable case 20 b is inintimate contact with the stationary base 20 a, a vacuum (negativepressure) can be produced in the vacuum chamber 20 by evacuating thevacuum chamber 20 by an evacuation system 23. A sealing member 20 c isfixed to a portion of the movable case 20 b which is brought intocontact with the stationary base 20 a.

[0042] The internal pressure forming apparatus is provided in the vacuumchamber 20 with a shaft forming die 30. The shaft forming die 30consists of an upper die 30 a and a lower die 30 b. The upper die 30 ais fixed to an inner surface of a top wall of the movable case 20 b,while the lower die 30 b is fixed on top of a lower-die platform (table)31 which is supported to be capable of moving up and down with respectto the stationary base 20 a while maintaining the airtightness betweenthe lower-die platform 31 and the stationary base 20 a. The upper die 30a and the lower die 30 b are provided on opposed surfaces thereof with apair of shaping recesses 32 a and 32 b, respectively, for accommodatingand pressing the composite body 10 therebetween to shape the compositebody 10 in a certain desired form. It is desirable that the upper die 30a and the lower die 30 b be provided, at respective ends of the pair ofshaping recesses 32 a and 32 b in the vicinity of large-diameter endsthereof (the right ends as viewed in FIG. 3), with upper and lowersemicircular circumferential grooves (or flanges) for clamping theperiphery of a large-diameter end (the right end as viewed in FIG. 1) ofthe internal-pressure holding tube 12, respectively, while the mandrel11 is provided with an annular flange (or groove) which can be engagedwith the upper and lower semicircular circumferential grooves (orflanges). The lower-die platform 31, which carries the lower die 30 b,is driven to ascend and descend by a lower-die raising/loweringmechanism 33 to move toward and away from the upper die 30 a (themovable case 20 b). Accordingly, in the illustrated embodiment of theinternal pressure forming apparatus, the lower-die raising/loweringmechanism 33 and the vacuum-chamber opening/closing mechanism 21constitute an opening/closing mechanism for opening and closing theshaft forming die 30.

[0043] The lower-die platform 31 is provided on top thereof with amandrel support device (composite-body support device) 40 consisting ofa cantilever support base 41 and an anti-deflection support base 42. Thecantilever support base 41 supports the large-diameter end of themandrel 11 in a manner to cantilever the composite body 10. Theanti-deflection support base 42 subsidiarily supports a small-diameterend (tip end) of the composite body 10 to prevent the small-diameter endthereof from developing deflections. The cantilever support base 41 isprovided with a front support portion (inner support portion) 41b and arear support portion (outer support portion) 41c positioned to be closerto the large-diameter end of the mandrel 11 than the front supportportion 41 b. The front support portion 41 b is provided thereon with ahalf-cylindrical recess 41 a having a radius corresponding to a half ofan outer diameter of the large-diameter end of the mandrel 11. The frontsupport portion 41 b is provided on an inner surface of thehalf-cylindrical recess 41 a with a half-cylindrical engaging projection41 a′ which corresponds to the axial-movement prevention groove 11 c tobe engageable therein. The rear support portion 41 c is providedadjacent to the half-cylindrical recess 41 a with a cantilever throughhole 41 d which is greater in diameter than the large-diameter end ofthe mandrel 11 so that only an upper edge of the rear support portion 41c in the cantilever through hole 41 d comes in contact with thelarge-diameter end of the mandrel 11 from above.

[0044] The front support portion 41 b is guided in a die-closingdirection of the shaft forming die 30 (vertical direction as viewed inFIG. 3) by a pair of guide shafts 41 e, and is continuously biasedupwards by two compression coil springs 41 f (see FIG. 11). The uppermoving limit of the front support portion 41 b with respect to thelower-die platform 31 is determined by a pair of stops 41 g fixed toupper ends of the pair of guide shafts 41 e, respectively (see FIG. 11).

[0045] The anti-deflection support base 42 is provided with a pair ofvertical pins 42 a between which the tip end (the left end as viewed inFIG. 1) of the composite body 10 is inserted. The pair of vertical pins42 a prevents the tip end of the composite body 10 from movinghorizontally (in the horizontal direction as viewed in FIG. 12). Themovable case 20 b is provided on an inner surface thereof with an upperanti-deflection member 42 c which is fixed to the movable case 20 b tocorrespond to the anti-deflection support base 42. The upperanti-deflection member 42 c is provided with a pair of clearance holes42 b in which the pair of vertical pins 42 a are respectively insertedwhen the movable case 20 b is driven to move down (see FIG. 12).

[0046] According to the mandrel support device 40 described above, ifthe large-diameter end of the composite body 10 (the mandrel 11) isinserted into the cantilever through hole 41 d of the rear supportportion 41 c and subsequently the engaging projection 41 a′ is engagedin the axial-movement prevention groove 11 c, the composite body 10 iscantilevered by the cantilever support base 41 to be supported thereby(i.e., in a manner so that the tip end of the composite body 10 stays inthe air as a free end) while the tip end of the composite body 10 isprevented from moving horizontally with the tip end of the compositebody 10 being positioned between the pair of vertical pins 42 a of theanti-deflection support base 42. In this state, if no external force isapplied to the front support portion 41 b, the front support portion 41b is positioned in a raised position thereof by the two compression coilsprings 41 f while the composite body 10 (the prepreg 13 thereof) isheld in a position thereof at which the composite body 10 is not incontact with the lower die 30 b (specifically, with the inner surface ofthe shaping recess 32 b).

[0047] On the other hand, the movable case 20 b is provided with anupper holding block 43 which is fixed to an inner surface of the movablecase 20 b to correspond to the front support portion 41 b of thecantilever support base 41. The upper holding block 43 serves as aholding device for holding the large-diameter end of the composite body10 between the upper holding block 43 and the front support portion 41 bof the cantilever support base 41. The upper holding block 43 is guidedin the die-closing direction of the shaft forming die 30 by a pair ofguide shafts 43 a, and is continuously biased downwards by twocompression coil springs 43 b which have a spring force greater than thetwo compression coil springs 41 f. The lower moving limit of the upperholding block 43 with respect to the movable case 20 b is determined bya pair of stops 43 c fixed to lower ends of the pair of guide shafts 43a, respectively (see FIG. 11). The upper holding block 43 is providedwith a half-cylindrical engaging projection 43 d which corresponds tothe axial-movement prevention groove 11 c which is engageable therein.The engaging projection 43 d together with the engaging projection 41 a′is engaged in the axial-movement prevention groove 11 c to prevent themandrel 11 (the composite body 10) from moving in the axial directionthereof when the lower-die platform 31 is raised while the movable case20 b is lowered.

[0048] A mechanism for injecting compressed air into the mandrel 11 ofthe composite body 10 in a state where the shaft forming die 30 isclosed after the vacuum chamber 20 is evacuated by the evacuation system23 will be hereinafter discussed with reference chiefly to FIGS. 9 and10. The movable case 20 b is provided with an intermediate movablenozzle (pipe) 51 whose opposite ends extend inside and outside themovable case 20 b and which is guided along the axis of the intermediatemovable nozzle 51 in an airtight fashion in a direction parallel to theaxis of the pair of shaping recesses 32 a and 32 b (i.e., the axis ofthe composite body 10). The intermediate movable nozzle 51 is providedat an inner end thereof with an insertion portion 51 a which is fittedinto the axial air passage 11 a of the mandrel 11, and two O-rings 51 bare fitted on the insertion portion 51 a with a predetermined gaptherebetween in the axial direction of the intermediate movable nozzle51. A compression coil spring 51 c for biasing the intermediate movablenozzle 51 in a direction to make the intermediate movable nozzle 51project outwards from the movable case 20 b (in a direction to make theintermediate movable nozzle 51 disengaged from the mandrel 11) is fittedon the portion of the intermediate movable nozzle 51 which is positionedoutside the movable case 20 b. An O-ring 51 d is fitted on the portionof the intermediate movable nozzle 51 which slides on an innerperipheral surface of the movable case 20 b in a thrust bearing hole(through hole) 20 d formed in the movable case 20 b.

[0049] The intermediate movable nozzle 51 is provided therein with acheck valve (one-way valve) 51 e. The check valve 51 e does not open bythe level of a negative pressure which is produced inside the vacuumchamber 20 (so that no air flowing into the vacuum chamber 20 isproduced). The check valve 51 e opens only when a forced valve-openingnozzle 52 is inserted into the intermediate movable nozzle 51 from theoutside open end thereof by an amount so that a pressing portion 52 afixed at the tip end of the forced valve-opening nozzle 52 presses thecheck valve 51 e inwards, toward the insertion portion 51 a. The forcedvalve-opening nozzle 52 is connected to an internal-pressure supplysystem (supply source) 53 (see FIG. 3), and is fixed to a movable plate52 c which is movable in the axial direction of the intermediate movablenozzle 51. The two O-rings 52 b maintain airtightness between theintermediate movable nozzle 51 and the forced valve-opening nozzle 52when the forced valve-opening nozzle 52 is inserted into theintermediate movable nozzle 51. The internal-pressure supply system 53,the forced valve-opening nozzle 52, and the intermediate movable nozzle51 constitute an internal-pressure supplying device.

[0050] The intermediate movable nozzle 51 and the forced valve-openingnozzle 52 are positioned so that the axes thereof are aligned when themovable case 20 b is closed. The axes of the intermediate movable nozzle51 and the composite body 10 are aligned when the shaft forming die 30is clamped after the movable case 20 b is closed. Although one shapingrecess 32 a and one shaping recess 32 b are illustrated on the upper die30 a and the lower die 30 b in the drawings, respectively, a series ofshaping recesses each corresponding to the shaping recess 32 a and acorresponding series of shaping recesses each corresponding to theshaping recess 32 b are actually formed on the upper die 30 a and thelower die 30 b, respectively, and also a plurality of cantilever supportbases each corresponding to the cantilever support base 41, a pluralityof anti-deflection support bases each corresponding to theanti-deflection support base 42 and a plurality of upper holding blockeach corresponding to the upper holding block 43 are providedaccordingly.

[0051] The vacuum-chamber opening/closing mechanism 21, the evacuationsystem 23, the lower-die raising/lowering mechanism 33, theinternal-pressure supply system 53 and a shaft forming die heatingsystem 34 are connected to a controller 60 (see FIG. 3). The controller60 controls operations of these systems/mechanisms connected thereto.

[0052] An embodiment of a shaft forming process performed by the presentembodiment of the internal pressure forming apparatus will behereinafter discussed.

[0053] Firstly, the composite body 10 shown in FIGS. 1 and 2, which isformed by covering the mandrel 11 with the internal-pressure holdingtube 12, and subsequently wrapping the prepreg 13 around this mandrel 11covered with the internal-pressure holding tube 12, is prepared.

[0054] Subsequently, the composite body 10 thus prepared is set to themandrel support device 40 to be supported thereby in a state where themovable case 20 b has been raised by the vacuum-chamber opening/closingmechanism 21 while the lower-die platform 31 (the lower die 30 b) hasbeen lowered by the lower-die raising/lowering mechanism 33 as shown inFIGS. 5A and 5B. Namely, the large-diameter end of the composite body 10(the mandrel 11) is inserted into the cantilever through hole 41 d ofthe rear support portion 41 c, the engaging projection 41 a′ is engagedin the axial-movement prevention groove 11 c, and the tip end of thecomposite body 10 is positioned between the pair of vertical pins 42 aof the anti-deflection support base 42. In this state, the compositebody 10 (the prepreg 13) is positioned immediately above the shapingrecess 32 b of the lower die 32 without contacting with an inner surfaceof the lower die 30 b in the shaping recess 32 b. The amount ofisolation of the composite body 10 from an inner surface of the shapingrecess 32 b of the lower die 30 b is determined so that the compositebody 10 does not come into contact with the inner surface of the shapingrecess 32 b in an evacuating operation using the evacuation system 23with consideration of the deformation (deviation) of the prepreg 13which is not yet heated. Specifically, a few millimeters is sufficientfor the amount of isolation of the composite body 10.

[0055] Subsequently, the movable case 20 b is lowered by thevacuum-chamber opening/closing mechanism 21 to form the vacuum chamber20 between the stationary base 20 a and the movable case 20 b, and thevacuum chamber 20 thus formed is evacuated by the evacuation system 23(see FIG. 6). After completion of this evacuation, the composite body 10(the prepreg 13) and the inner surface of the shaping recess 32 b do notcontact each other by an amount S, as shown in FIG. 5B. In theevacuating operation using the evacuation system 23, it is desirablethat the air which exits between the prepreg 13 of the composite body 10and the internal-pressure holding tube 12 be vacuumed so as to beremoved therefrom; moreover, it is desirable that the air in the prepreg13 be also vacuumed so as to be removed therefrom. Removing this airreliably prevents the air from being trapped on a surface of the prepreg13 and thereby deteriorating the surface irregularity (surfaceroughness) of the prepreg 13. To this end, it is desirable that enoughtime be provided for the evacuating operation or that the composite body10 be moved into the vacuum chamber 20 after the composite body 10 isput into an auxiliary vacuum tank (not shown).

[0056] Immediately after the amount of vacuum in the vacuum chamber 20exceeds a predetermined level (e.g., 0.01 kg/cm²; a pressure ofapproximately 800 pascals), the lower-die platform 31 (the lower die 30b) is raised to close the shaft forming die 30. This upward movement ofthe lower-die platform 31 causes the mandrel support device 40 (whichconsists of the cantilever support base 41 and the anti-deflectionsupport base 42) on the lower-die platform 31 to move upward togetherwith the lower-die platform 31, and causes the front support portion 41b of the cantilever support base 41 to move downward slightly withrespect to the lower-die platform 31 while compressing the compressioncoil springs 41 f, and at the same time causes the anti-deflectionsupport base 43 to move upward slightly while compressing thecompression coil springs 43 b so that the mandrel 11 (the composite body10) is held between the cantilever support base 41 and theanti-deflection support base 43 without moving in the axial direction ofthe mandrel 11 (the composite body 10). In this state, the prepreg 13 ofthe composite body 10 is in contact with inner surfaces of the upper die30 a and the lower die 30 b in the pair of shaping recesses 32 a and 32b. At this time, substantially no air exits between the prepreg 13 andthe pair of shaping recesses 32 a and 32 b (see FIG. 7) since the air inthe vacuum chamber 20 has been sufficiently vacuumed by this time.

[0057] On completion of the clamping operation of the shaft forming die30, the movable plate 52 c is moved toward the movable case 20 to insertthe tip end of the forced valve-opening nozzle 52 into the intermediatemovable nozzle 51 to thereby open the check valve 51 e via the pressingportion 52 a. Subsequently, the movable plate 52 c is further movedtoward the movable case 20 to further insert the tip end of the forcedvalve-opening nozzle 52 into the intermediate movable nozzle 51 toinsert the insertion portion 51 a of the intermediate movable nozzle 51into the axial air passage 11 a of the mandrel 11 (see FIGS. 7 and 10).This operation does not make the composite body 10 move in the axialdirection thereof because the composite body 10 is prevented from movingin the axial direction thereof by the engagement of the engagingprojection 41 a′ with the axial-movement prevention groove 11 c and theengagement of the engaging projection 43 d with the axial-movementprevention groove 11 c. In this state, applying pressure to the insideof the internal-pressure holding tube 12 through the axial air passage11 a and the plurality of radial air passages 11 b by theinternal-pressure supplying system 53 to increase the internal pressurein the internal-pressure holding tube 12 causes the prepreg 13 to comeinto intimate contact with inner surfaces of the upper die 30 a and thelower die 30 b in the pair of shaping recesses 32 a and 32 b. Since theshaft forming die 30 has been heated to a predetermined temperature bythe shaft forming die heating system 34 at this stage, the prepreg 13 isshaped to correspond to the shape of the pair of shaping recesses 32 aand 32 b by maintaining the temperature of the shaft forming die 30 at apredetermined degree for a predetermined period of time in a state wherethe shaft forming die 30 is closed.

[0058] After completion of the formation of the composite body 10, thevalve-opening nozzle 52 is removed from the intermediate movable nozzle51 to introduce the air to the inside of the vacuum chamber 20.Thereafter, the lower-die platform 31 is lowered to open the shaftforming die 30, and the movable case 20 b is opened to remove a moldedshaft 13′ together with the mandrel 11 (see FIG. 8). Subsequently, themandrel 11 and the internal-pressure holding tube 12 are removed in thatorder from the inside of the molded shaft 13′. It is possible to leavethe internal-pressure holding tube 12 inside the molded shaft 13′. Inthis case, it is desirable that the internal-pressure holding tube 12 bemade of a plastic film.

[0059] A manner of supporting the vacuum chamber 20 and the shaftforming die 30 has been discussed above by way of example. The vacuumchamber 20 can be an unopenable chamber as long as necessary operationscan be carried out inside the vacuum chamber. The mandrel support.device 40 can be driven independently of the shaft forming die 30 (theupper die 30 a and the lower die 30 b). In addition, the upper holdingblock 43 can be fixedly mounted to an inner surface of the movable case20 b though provided to be movable with respect to an inner surface ofthe movable case 20 b in the above illustrated embodiment of the mandrelsupport device 40.

[0060] Although the composite body 10 is composed of the mandrel 11, theinternal-pressure holding tube 12 and the prepreg 13 in the abovedescribed embodiment of the internal pressure forming apparatus, theinternal-pressure holding tube 12 and the prepreg 13 are fundamentalelements at the shaft forming operation. Namely, the mandrel 11 does nothave to exist at the formation of the shaft 13′. FIG. 13 shows acomposite body 10′, wherein the mandrel 11 is removed from the compositebody 10′ after the prepreg 13 is wrapped around the internal-pressureholding tube 12, and an air-injecting mouth piece 11′ is airtightlyfixed to an open end of the internal-pressure holding tube 12 instead.In the case of using the composite body 10′ shown in FIG. 13, a hollowFRP article can be formed by the same procedures as those describedabove with the above described embodiment of the internal pressureforming apparatus.

[0061] The present invention can be applied not only to a method and anapparatus for forming a hollow FRP golf club shaft by internal pressuremolding such as those described above, but also to a method and anapparatus for forming any hollow FRP article such as a ski pole. Inaddition, the present invention can also be applied to a method and anapparatus for forming a non-linear hollow FRP article such as a hockeystick. Although the mandrel basically needs to have a shapecorresponding to the shape of the associated forming die, the mandrelcan be of a type having a length smaller than the length of a hollowarticle which is to be formed by the internal pressure forming apparatusaccording to the present invention. Namely, since the shape of thehollow article is determined by the shape of the forming die, the shapeof the mandrel itself does not need to exactly correspond to the shapeof the hollow article; for instance, the mandrel can be composed of aplurality of separate pieces. Alternatively, the mandrel can be made ofmetal having a high elasticity such as lead in the case of forming anon-linear hollow article so that the mandrel can be removed from thenon-linear hollow article after the formation thereof, or the mandrelcan be made of wax or a similar material which is melted when heatedaccording to a method such as a lost wax process.

[0062] As can be understood from the foregoing, according to the presentinvention, a hollow FRP article with a satisfactory surface irregularityis achieved by internal pressure molding with which vacuum forming ismerged.

[0063] Obvious changes may be made in the specific embodiments of thepresent invention described herein, such modifications being within thespirit and scope of the invention claimed. It is indicated that allmatter contained herein is illustrative and does not limit the scope ofthe present invention.

What is claimed is:
 1. A method for forming a hollow FRP article byinternal pressure molding, comprising: positioning a FRP prepreg on aperiphery of an airtight internal-pressure holding tube; inserting acomposite body including said internal-pressure holding tube and saidprepreg into a vacuum chamber containing a forming die; evacuating saidvacuum chamber in an isolation state where said composite body and saidforming die do not contact each other; and clamping said forming die tobring said forming die and said composite body into contact with eachother and heating said forming die with an application of pressure to aninside of said internal-pressure holding tube after completion of saidevacuating step.
 2. The FRP hollow article forming method according toclaim 1, wherein said prepreg positioning step comprises: covering amandrel with said internal-pressure holding tube; and wrapping said FRPprepreg around said periphery of said internal-pressure holding tube. 3.The FRP hollow article forming method according to claim 2, wherein saidclamping and heating step comprises applying pressure to said inside ofsaid internal-pressure holding tube through air passages formed on saidmandrel.
 4. The FRP hollow article forming method according to claim 1,wherein said prepreg positioning step comprises: covering a mandrel withsaid internal-pressure holding tube; wrapping said FRP prepreg aroundsaid periphery of said internal-pressure holding tube; and removing saidmandrel after said wrapping step.
 5. The FRP hollow article formingmethod according to claim 4, wherein said clamping and heating stepcomprises applying pressure to said inside of said internal-pressureholding tube through an air-injecting mouth piece fixed to an open endof said internal-pressure holding tube after said mandrel is removed. 6.An apparatus for forming a hollow FRP article by internal pressuremolding, comprising: a vacuum chamber; a forming die positioned in saidvacuum chamber; a vacuum-chamber opening/closing mechanism for openingand closing said vacuum chamber; a composite-body support device forsupporting a composite body without making said composite body come intocontact with said forming die in a state where said forming die isopened by said vacuum-chamber opening/closing mechanism, said compositebody including an airtight internal-pressure holding tube and a prepregfitted on said airtight internal-pressure holding tube; an evacuationsystem for evacuating said vacuum chamber; an internal-pressuresupplying device for applying pressure to an inside of saidinternal-pressure holding tube of said composite body which is supportedby said composite-body support device; and a controller for actuatingsaid vacuum-chamber opening/closing mechanism to clamp said forming dieto thereby bring said forming die and said composite body into intimatecontact with each other, and for heating said forming die with anapplication of pressure to said inside of said internal-pressure holdingtube after said vacuum chamber is evacuated by said evacuation system.7. The FRP hollow article forming apparatus according to claim 6,wherein said composite body is obtained by covering a mandrel with saidinternal-pressure holding tube and wrapping said FRP prepreg around aperiphery of said internal-pressure holding tube.
 8. The FRP hollowarticle forming apparatus according to claim 7, wherein said mandrelcomprises an axial air passage and at least one radial air passage, andwherein said internal-pressure supplying device comprises: anintermediate movable nozzle which is removably inserted into said axialair passage and includes a one-way valve for preventing air from flowinginto said vacuum chamber; a forced valve-opening nozzle which isremovably inserted into said forced valve-opening nozzle, said one-wayvalve being opened by an insertion of said forced valve-opening nozzleinto said intermediate movable nozzle; and an internal-pressuresupplying source for supplying compressed air to said forcedvalve-opening nozzle.
 9. The FRP hollow article forming apparatusaccording to claim 6, wherein said composite body is obtained bycovering a mandrel with said internal-pressure holding tube, wrappingsaid FRP prepreg around a periphery of said internal-pressure holdingtube, and thereafter removing said mandrel from said composite body. 10.The FRP hollow article forming apparatus according to claim 9, whereinsaid mandrel comprises an axial air passage and at least one radial airpassage, and wherein said internal-pressure supplying device comprises:an intermediate movable nozzle which is removably inserted into saidaxial air passage after said removal of said mandrel from said compositebody, and includes a one-way valve for preventing air from flowing intosaid vacuum chamber; a forced valve-opening nozzle which is removablyinserted into said forced valve-opening nozzle, said one-way valve beingopened by an insertion of said forced valve-opening nozzle into saidintermediate movable nozzle; and an internal-pressure supplying sourcefor supplying compressed air to said forced valve-opening nozzle. 11.The FRP hollow article forming apparatus according to claim 6, whereinsaid composite-body support device comprises a cantilever support basefor supporting said composite body in a cantilever fashion.
 12. The FRPhollow article forming apparatus according to claim 6, wherein saidcomposite-body support device is mounted to a lower-die table whichsupports a lower die of said forming die thereon, and wherein at least apart of said composite-body support device is biased upwards, toward anupward moving limit thereof, by a biasing device so that said compositebody, which is supported by said composite-body support device, does notcontact said lower die.
 13. The FRP hollow article forming apparatusaccording to claim 6, wherein said forming die and said composite bodyare designed for manufacturing a golf club shaft.
 14. The FRP hollowarticle forming apparatus according to claim 11, wherein said compositebody is obtained by covering a mandrel with said internal-pressureholding tube and wrapping said FRP prepreg around a periphery of saidinternal-pressure holding tube; wherein said cantilever support baseincludes an inner support portion and an outer support portion which arepositioned apart from each other in an axial direction of said compositebody; wherein said inner support portion includes a half-cylindricalrecess having a radius corresponding to a half of an outer diameter of alarge-diameter end of said mandrel, a portion of said mandrel in avicinity of said large-diameter end being positioned in saidhalf-cylindrical recess; and wherein said outer support portion includesa cantilever through hole which is greater in diameter than saidlarge-diameter end of said mandrel so that only an upper edge of saidouter support portion in said cantilever through hole comes in contactwith said large-diameter end of said mandrel from above.
 15. The FRPhollow article forming apparatus according to claim 14, wherein saidcomposite-body support device further comprises an anti-deflectionsupport base, positioned inside said vacuum chamber, for subsidiarilysupporting a small-diameter end of said composite body to prevent saidsmall-diameter end from developing deflections.
 16. The FRP hollowarticle forming apparatus according to claim 15, wherein said lower-dietable is guided in a vertical direction to be movable vertically withrespect to an upper die fixed to an inner surface of said vacuumchamber.